1. Field of the Invention
The present invention relates generally to a microwave switch, and more particularly it relates to a microwave DPDT (Double-Pole Double-Throw) switch, a microwave divide/through switch, and a highly efficient power amplifier using the divide/through switch.
2. Description of the Related Art
Microwave and millimeter-wave switches are widely used components in wireless circuit such as phase shifters, phase-array antenna, transceivers, QPSK (Quadrature Phase Shift Keying) and PSK (Phase Shift Keying) system. Most of known microwave switches are FETs (field effect transistors) and PIN diodes, since they can be made in the same process as MMIC (Microwave Monolithic Integrated Circuit). But these kinds of microwave switches have high insertion losses, poor isolation, inevitable nonlinearity, and standing power property.
To resolve the above shortcomings, Larson et. al. reported a microwave switch in the early 1990""s, which needed high initial voltages larger than about 100 V to operate, composed of micro-motors. J. Yao et. al. showed a switch of cantilever type which had a 50 dB isolation and a 0.1 dB insertion loss at 4 GHz. Its switching voltage and closure time are 28 V and 30 xcexcs, respectively. This switch is of series and resistance type. Goldsmith et. al. presented a switch of shunt and capacitor type, and Pacheco et. al. did an anti-vibration switch.
Most of micro-machined microwave switches are much slower than PIN diodes and FET (field effect transistor) switches and need higher switching voltages. And the handling powers are also smaller than their semiconductor counterparts. But microwave switches show low insertion losses (xe2x89xa60.5 dB) at the on-state, and high isolation (xe2x89xa740 dB) at the off-state. When they are not activated, there is no power consumption. In addition, they have no nonlinearity at all. Due to these advantages, they are used beneficially in the RF communication systems.
And since double-pole double-throw (DPDT) switches used frequently in microwave systems have complicated structures needing four SPST (Single-Pole Single-Throw) switches as displayed in FIG. 1, it is necessary to simplify the structures.
Meanwhile, general balance power amplifiers are composed of two amplifiers and two branch line couplers as displayed in FIG. 2 in order to give balance property of the power amplifiers. These balance power amplifiers have a disadvantage of low efficiencies when the average powers of input signals are much lower than maximum available powers of the amplifiers.
It is an object of the present invention to provide (1) a microwave DPDT switch routing two input signals into two output signals with simple structure, (2) a microwave divide/through switch dividing the input signal into two output signals or transmitting an input signal into a single output signal, and (3) a highly efficient power amplifier of balance property using the divide/through switch instead of branch line coupler.
The microwave DPDT switch according to the present invention is composed of (1) a branch line coupler having three gaps at the branch lines among two input and two output ports, and (2) three SPST switches locating at the three branch line gaps to transmit input signals to the output ports.
The microwave divide/through switch according to the present invention, dividing or transmitting input signals to the output ports, is composed of (1) a 90xc2x0 branch line coupler having two gaps at the branch lines among two input and output ports, and (2) two SPST switches locating at the two branch line gaps to transmit input signals to the output ports.
The highly efficient power amplifier according to the present invention is composed of (1) the two microwave divide/through switches, (2) two power amplifiers, connected with the two microwave divide/through switches, to amplify the signal power transmitted from the first microwave divide/through switch, and (3) a half-wavelength transformer, connected to an output of one of the power amplifiers, to delay the phase of the amplified signal by a half-wavelength.